This chapter introduces two techniques for documenting business processes- Data Flow Diagrams (DFD's) and System Flowcharting (SFC). It discusses how to read these documents, their purpose, and guidelines for creating DFD's and SFC's from narratives (see discussion)
Data Flow Diagrams:
A data flow diagram(DFD) is a graphical representation of a system. A DFD depicts a system's components; the data flow among components; and the sources, destinations, and storage of data.
Types of Dataflow Diagrams (define and explain the differences):
Physical - is a graphical representation of a system showing the system’s internal and external entities, and the flows of data into and out of these entities. Physical DFDs specify where, how, and by whom a system’s processes are accomplished. A physical DFD does not tell us what is being accomplished.
Logical - is a graphical representation of a system showing the system’s processes (as bubbles), data stores, and the flows of data into and out of the processes and data stores. Logical DFDs are used to document information systems because the logical nature of a system—what tasks the system is doing—can be represented without having to specify how, where, or by whom the tasks are accomplished.
The advantage of a logical DFD over a physical DFD is that we can concentrate on the functions that a system performs. A logical DFD portrays a syatems activities whereas a physical DFD depict a system's infrastructure.
Levels of Dataflow Diagrams:
Context - A top-level, least detailed, diagram of an IS that depicts a system and all of its activities within a single bubble. Data flows into and out of the system, and into and out of the external entities are also shown.
Level-0 - A level lower than the context diagram, which explodes the context diagram bubble to see the major subdivision of the process. For example, if there are 3 subdivision of the process, it is coded as 1.0, 2.0 3.0. The successive subdividing, or "exploding" of logical DFDs is called top-down partioning and, when properly performed leads to a balanced set of DFDs.
Level-1 - Under each subprocess in Level 0, further details of that subprocess, say 1.0, can be described by using 1.1, 1.2, 1.3, and etc.
Level-x (How low can you go?) In theory there is no limit as long as it is balanced. It depends on the complexity of the process, however, in practice, up to 3 to 4 levels are normally used.
Balanced Data Flow Diagram set - All DFDs in a set have the same number of external data flows. For example, if the Context diagram has 2 data flows from the source and 3 to the sink; all subsequent (Level-0, Level-1, etc) DFDs must also have 2 data flows from the source and 3 to the sink.
Data Flow Diagram Symbols:
Bubble (Physcial or Logical) - Represents an entity or a process within which incoming data flows are transformed into outgoing data flows.
Arrow - Represents a pathway for data.
Box - Represents an External entity. A source or destination (sink) of data outside of the system.
Open-ended Rectangle - Data store - represents a place where data are stored.
Preparing Systems Documentation:
Table of Entities and Activities (describe the steps for creation):
1. Read the narrative and underline circle or otherwise mark the entities and activities contained within the narrative
2. Number each paragraph or line in the narrative
3. Make a list of each entity and its associated activity along with the paragraph or line number from the narrative
Key Vocabulary for preparing Data Flow Diagrams:
· Activity- any action being preformed by an internal or external entity. Activities can include actions related to data or to an operations process.
GuideLines to Preparing DFDs:
1. Include within the system context(bubble) any entity that performs one or more information processing activities.
2. For now, include only normal processing routines, not exception routines or errors.
3. Include only entities and activities described in the narratives- no more, no less.
4. When multiple entities operate identically, depict one to represent all.
5. Draw a data flow for each flow into and out of a data store.
6. If a data store is logically necessary, include a data stores in the diagrams, even if not mentioned in the narratives.
7. Group activities if they occur in the same place and at the same time.
8. Group activities if they occur at the same time but in different places.
9. Group activities that seem to be logically related.
10. To make the DFD readable, use between 5 to 7 bubbles.
11. A data flow should go to operations process entity square only when operations process functions are to be performed by that entity. A data flow should enter an entity bubble if the operations process entity is to perform an operation processing activity.
12. On a physical DFD, reading computer data stores and writing to computer data stores must go through a computer bubble.
13. On a logical DFD, data flows cannot go from higher -to-lower-numbered bubbles.
Systems Flowcharts:
A systems flowchart(SFC) is a graphical representation of information processes and operations processes in a system.
A systems flowchart presents the who, what how and where of the information and operations processes. It provides a complete picture of a system by combining the physical and logical aspects into a single diagram.
Preparing Systems Flowcharts:
Divide the flowchart by creating a separate column for each internal or external entity that performs information processing.
Lay columns out so that there a minimum of crossed lines while preserving a left to right flow.
Flowchart logic should flow from top to bottom and left to right.
Strive to key the flowchart on a single page.
Do not directly connect documents in the same column.
When moving from one column to the next, show a document at both ends.
Sequential processing steps with no delay between them can be shown as a single process.
Access to a computer datastore is only possible through a computer processing rectangle.
No manual process in necessary to show sending nor filing a document.
Documents that are together should be placed on top of each other with the upper right edges sticking out from the documents behind.
Documenting Information Systems:
This chapter introduces two techniques for documenting business processes- Data Flow Diagrams (DFD's) and System Flowcharting (SFC). It discusses how to read these documents, their purpose, and guidelines for creating DFD's and SFC's from narratives (see discussion)Data Flow Diagrams:
A data flow diagram(DFD) is a graphical representation of a system. A DFD depicts a system's components; the data flow among components; and the sources, destinations, and storage of data.Types of Dataflow Diagrams (define and explain the differences):
Levels of Dataflow Diagrams:
Data Flow Diagram Symbols:
Preparing Systems Documentation:
Table of Entities and Activities (describe the steps for creation):
1. Read the narrative and underline circle or otherwise mark the entities and activities contained within the narrative2. Number each paragraph or line in the narrative
3. Make a list of each entity and its associated activity along with the paragraph or line number from the narrative
Key Vocabulary for preparing Data Flow Diagrams:· Activity- any action being preformed by an internal or external entity. Activities can include actions related to data or to an operations process.
GuideLines to Preparing DFDs:
1. Include within the system context(bubble) any entity that performs one or more information processing activities.2. For now, include only normal processing routines, not exception routines or errors.
3. Include only entities and activities described in the narratives- no more, no less.
4. When multiple entities operate identically, depict one to represent all.
5. Draw a data flow for each flow into and out of a data store.
6. If a data store is logically necessary, include a data stores in the diagrams, even if not mentioned in the narratives.
7. Group activities if they occur in the same place and at the same time.
8. Group activities if they occur at the same time but in different places.
9. Group activities that seem to be logically related.
10. To make the DFD readable, use between 5 to 7 bubbles.
11. A data flow should go to operations process entity square only when operations process functions are to be performed by that entity. A data flow should enter an entity bubble if the operations process entity is to perform an operation processing activity.
12. On a physical DFD, reading computer data stores and writing to computer data stores must go through a computer bubble.
13. On a logical DFD, data flows cannot go from higher -to-lower-numbered bubbles.
- Systems Flowcharts:
A systems flowchart(SFC) is a graphical representation of information processes and operations processes in a system.A systems flowchart presents the who, what how and where of the information and operations processes. It provides a complete picture of a system by combining the physical and logical aspects into a single diagram.
Preparing Systems Flowcharts: